Dental caries is, in a sense, an oral infection which is developed by the adherence and colonization of pathogenic bacteria onto the tooth surface. The mechanism for the colonization of oral bacteria on the tooth surface appears to be as follows. First, initial colonizing bacteria such as Streptococcus oralis, Streptococcus sanguis, Streptococcus gordonii, and Actinomyces naeslundii adsorb onto the enamel surface covered with a thin film (pellicle) of saliva. Then, as these initial colonizing bacteria grow, they coaggregate and start to accumulate plaque. Subsequently, as the plaque matures, the microbial flora shifts from facultative anaerobes to obligate anaerobes, and the obligate anaerobes represented by Fusobacterium nucleatum coaggregate with the initial colonizing bacteria. Then, periodontal disease-related bacteria such as Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia further coaggregate with the Fusobacterium nucleatum and colonize. Takemoto et al. further suggest that dental caries-related bacteria such as Streptococcus mutans and Streptococcus sobrinus have the same colonization mechanism because they also coaggregate with Fusobacterium nucleatum (Non Patent Literature 1).
As described above, the coaggregation of dental caries pathogens such as Fusobacteria and periodontal disease-related bacteria is deeply involved in the generation, development, and progression of dental caries, periodontal disease, halitosis, and the like. As a compound having an effectively inhibiting action on such coaggregation, an alkyl galactoside in which an alkyl group is ether-bonded to galactose is known. In Patent Literature 1, such a compound is used to obtain an oral composition having an inhibiting effect on dental caries and plaque accumulation. Further, in Patent Literature 2, the above alkyl galactoside and a nonionic bactericide are used in combination to obtain an oral composition that has a coaggregation-inhibiting action on Fusobacteria or the like and specifically kills bacteria belonging to the genus Fusobacterium.     (Patent Literature 1) JP-A-2006-124384    (Patent Literature 2) JP-A-2007-291083    (Non Patent Literature 1) Journal of Periodontal Research, Vol. 30, p 252-257